Multi-connection, non-simultaneous frequency diversity in radio communication systems

ABSTRACT

A radio communication system includes a remote device radio, and a base station radio operable to communicate with the remote device radio at a first channel and at a second channel using non-simultaneous frequency diversity. The base station is operable to communicate with a device other than the remote device at the second channel while the remote device radio and the base station radio are communicating at the first channel. A radio using non-simultaneous frequency diversity includes an antenna, a radio frequency module coupled to the antenna such that the radio frequency module is operable to transmit or receive radio frequency signals at a first channel and signals at a second channel using the antenna, and a baseband module coupled to the radio frequency module. The baseband module operable to transmit or receive signals through the radio frequency module, such that signals transmitted or received by the radio employ non-simultaneous frequency diversity using the first channel and the second channel. Additional devices are operable to use the second channel while the radio is transmitting or receiving radio frequency signals at the first channel.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to co-pending U.S. application Ser. No.______ titled “NON-SIMULTANEOUS FREQUENCY DIVERSITY IN RADIOCOMMUNICATION SYSTEMS” and filed concurrently herewith, which is herebyincorporated by reference in its entirety for all purposes.

TECHNICAL FIELD

This disclosure is directed to a radio communication system and, moreparticularly, to the use of diversity techniques to improve theperformance of radio communications in a multi-connection environment.

BACKGROUND

In radio communication systems, such as, for example, mobile telephonesystems and wireless networks, signals propagate through communicationchannels that are affected by a variety of factors including:atmosphere, man-made structures, terrain, fauna, and radio interference.As signals encounter man-made and natural objects, they may bereflected, refracted, and/or diffracted, resulting in changes inamplitude, phase, and frequency. To confound matters, a signal may reacha receiver through multiple paths, undergoing different distortionsalong each path. With differing phases and amplitudes, the multipathsignals may interfere with one another, further degrading signalquality. Signal attenuation caused by multipath interference orinteractions with man-made and natural object is called fading. A deepfade occurs when signal power drops so low as to prevent communications.

Because propagation channels are ever changing, fading is timedependent. Because the effects of reflection, refraction, anddiffraction are frequency dependent, fading also is frequency dependent.One solution to the problem of fading is the use of diversitytechniques—transmitting duplicate information such that the probabilityof fading disrupting signal reception is reduced.

Frequency diversity is sometimes used to reduce the likelihood of deepfade. Taking advantage of the frequency-dependent nature of fading,duplicate information is transmitted at different frequencies. As longas both frequency components are not in deep fade, communications canoccur.

Time diversity also is used to reduce the likelihood of deep fade. Bytransmitting duplicate information at a later time, the information ismore likely to be received because channel fading likely to differ. Tomaximize the effectiveness of time diversity, duplicate informationshould be transmitted after sufficient delay such that the fadingcharacteristics of the communications channel have sufficient time tochange.

Additional diversity techniques include path diversity and polarizationdiversity. By exploiting one or more diversity techniques, modem radiocommunication systems can significantly mitigate fading.

SUMMARY

In one general aspect, a radio communication system includes a remotedevice radio, and a base station radio operable to communicate with theremote device radio at a first channel and at a second channel usingnon-simultaneous frequency diversity. The base station is operable tocommunicate with a device other than the remote device at the secondchannel while the remote device radio and the base station radio arecommunicating at the first channel.

In some implementations, the remote device radio is a subscriber stationin a wireless network and the base station radio is a base station in awireless network. The system also may include a second remote deviceradio such that the base station radio is operable to communicate withthe remote device radio at the first channel while communicating withthe second remote device radio at the second channel. The remote deviceradio may include a single transmit/receive path.

Additionally, the radio communication system includes two communicationchannels with a frequency separation to facilitate non-simultaneousfrequency diversity (e.g., a frequency separation of over 20 MHz). Theinformation transmitted on the first and second channels may differ by acomplex gain. The first transmission channel and the second transmissionchannel may be wideband channels.

In another general aspect, a radio using non-simultaneous frequencydiversity includes an antenna, a radio frequency module coupled to theantenna such that the radio frequency module is operable to transmit orreceive radio frequency signals at a first channel and signals at asecond channel using the antenna, and a baseband module coupled to theradio frequency module. The baseband module operable to transmit orreceive signals through the radio frequency module, such that signalstransmitted or received by the radio employ non-simultaneous frequencydiversity using the first channel and the second channel. Additionaldevices are operable to use the second channel while the radio istransmitting or receiving radio frequency signals at the first channel.

In some implementations, the radio includes a second antenna coupled tothe radio frequency module. The radio frequency module may beimplemented using a local oscillator operable to generate a signal, anintermediate frequency receiver, an intermediate frequency transmitter,a receive mixer coupled to the intermediate frequency receiver and thelocal oscillator, and a transmit mixer coupled to the intermediatefrequency transmitter and the local oscillator. The receive mixer andthe transmit mixer convert signals between an intermediate frequency anda transmission frequency using the local oscillator signal. In otherimplementations, a zero-if mixer may be employed to convert signals frombaseband frequencies to transmission frequencies using a localoscillator.

Additionally, the radio may be operable to transmit data usingnon-simultaneous frequency diversity by using the local oscillator totransmit data at a first frequency and by using the local oscillator totransmit data at a second frequency. In some implementations, it may bedesirable for the receive mixer, the local oscillator, and theintermediate frequency receiver to form a receive path such that theradio employs non-simultaneous frequency diversity using a singlereceive path. Alternatively, the radio may further include a secondlocal oscillator such that the radio is operable to transmit data usingnon-simultaneous frequency diversity by using the local oscillator totransmit data at a first frequency and by using the second localoscillator to transmit data at a second frequency. The baseband modulemay use orthogonal frequency division multiplexing (OFDM).

In another general aspect, a method for transmitting information usingnon-simultaneous frequency diversity includes identifying information tobe transmitted to a first device, transmitting the identifiedinformation to the first device on a first channel while simultaneouslycommunicating with a second device on the second channel, and, after apredetermined amount of time, transmitting the identified information ona second channel.

In some implementations, identifying information to be transmittedincludes identifying a block to be transmitted from a set of informationto be transmitted. The block includes no more than the maximum amount ofinformation that can be transmitted at one time. For example, the sizeof the block may be based on the size of an orthogonal frequencydivision multiplexing (OFDM) tone.

The identified information may be transmitted at the first or secondfrequencies by mixing an intermediate frequency signal with the outputfrom a local oscillator to convert the intermediate frequency signal tothe transmission frequency. The same local oscillator may be used forboth. In addition, the predetermined amount of time betweentransmissions may be fixed or dynamic. The radio may be configured totransmit signals on the first transmission channel and to transmitsignals on the second transmission channel at consecutive points intime.

In another general aspect, a method for receiving informationtransmitted using non-simultaneous frequency diversity includesreceiving a first signal transmitted by a first device on a firstchannel while simultaneously communicating with a second device on asecond channel, receiving a second signal transmitted by the firstdevice on the second channel after a predetermined amount of time, andidentifying transmitted information based on the first signal and thesecond signal.

In some implementations, the method further includes converting thefirst signal to an intermediate frequency using a signal from a localoscillator, and converting the second signal to an intermediatefrequency using a signal from a local oscillator. The same localoscillator may be used to convert both the first signal and the secondsignal. The amount of time between reception of the first signal and thesecond signal may be fixed or dynamic.

Implementations may include using a single receive path to receive thefirst signal transmitted on the first channel and to receive the secondsignal transmitted on a second channel. The first channel and the secondchannel may be wideband channel, and the first channel and the secondchannel differ by at least 20 MHz.

The system may identify the transmitted information by combining thefirst signal and the second signal using selection diversity, equal gaincombining, and/or maximal ratio combining.

In another general aspect, a method for receiving informationtransmitted using non-simultaneous frequency diversity includesreceiving a first signal transmitted by a first device on a firstchannel while a second device communicates on a second channel,receiving a second signal transmitted by the first device on the secondchannel after a predetermined amount of time, and identifyingtransmitted information based on the first signal and the second signal.The first device may be a base station in a wireless network such that atransmission from the first device is received while the second devicecommunicates with the first device.

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features andadvantages will be apparent from the description and drawings, and fromthe claims.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram of a radio communication system.

FIG. 2 is an amplitude-versus-frequency plot of a radio communicationsystem transmission using simultaneous frequency diversity.

FIGS. 3A and 3B are amplitude-versus-frequency plots of radiocommunication system transmissions using non-simultaneous frequencydiversity.

FIG. 3C is an amplitude-frequency-time graph of a series oftransmissions using non-simultaneous frequency diversity.

FIG. 4A is an amplitude-versus-frequency plot of a radio communicationsystem transmission using orthogonal frequency division multiplexing(OFDM).

FIG. 4B is a block diagram of OFDM transmissions at various points intime illustrating non-simultaneous frequency diversity.

FIG. 5A is a block diagram of a radio using non-simultaneous frequencydiversity.

FIG. 5B is a block diagram of the radio frequency (RF) stage of a radiousing non-simultaneous frequency diversity.

FIG. 6A is a block diagram of a multi-connection system usingnon-simultaneous frequency diversity.

FIG. 6B is an amplitude-frequency-time plot of a multi-connection radiocommunication system transmission using non-simultaneous frequencydiversity.

FIG. 7A is a flow chart of a method of transmitting information usingnon-simultaneous frequency diversity.

FIGS. 7B and 7C are flow charts of methods of receiving informationtransmitted using non-simultaneous frequency diversity.

DETAILED DESCRIPTION

Referring to FIG. 1, a radio communication system 100 comprises a basestation 102 operable to communicate with multiple remote stations 104.The base station 102 is coupled to a network 106 such that the basestation 102 can transfer information between the network 106 and theremote stations 104. The radio communication system 100 may be used toprovide wireless services, such as, for example, wireless metropolitanarea networks, wireless local area networks, wireless video-on-demand,and/or wireless voice services.

For example, the radio communication system 100 may be used to implementa wireless local area network (WLAN) based on the IEEE 802.11 standard.In this implementation, the base station 102 serves as an access pointor as a router, connecting one or more remote stations 104 to a network106, which can be a local area network (LAN) or a wide area network(WAN), such as the Internet. The remote stations 104 typically arelaptop or desktop computers configured with wireless network interfacecards.

The base station 102 is a hardware device that facilitates radiofrequency (RF) communications with remote stations 104. The RFcommunications is typically two-way (with the base station 102 andremote station 104 transmitting and receiving information from oneanother); however, the non-simultaneous frequency diversity techniquesdescribed herein may also be used with one-way RF communications, suchas, for example, a video or information broadcast system, or a pagersystem.

To facilitate two-way RF communications, the base station 102 includesat least one antenna and a signal processing unit. The signal processingunit typically includes components to filter and amplify signals, toconvert signals between analog and digital, and to interpret and processreceived data.

The base station 102 and remote stations 104 may be implemented usingconventional electronic design and manufacturing techniques usingapplication-specific integrated circuits and/or commercial off-the-shelfcomponents. Portions of the implementations may be carried out insoftware-configured digital signal processors (DSPs) or general-purposemicroprocessors.

To improve performance, a variety of diversity techniques may beemployed including frequency diversity. According to the Glossary ofTelecommunication Terms (Federal Standard 1037 (2000)), frequencydiversity is “transmission and reception in which the same informationsignal is transmitted simultaneously on two or more independently fadingcarrier frequencies.” Because fading typically is frequency-dependent,frequencies near one another are not likely to fade independently. Forthis reason, it is useful to choose two or more disparate carrierfrequencies. However, using disparate carrier frequencies may increaseimplementation expense and complexity.

Referring to FIG. 2, a radio communication system 100 employingsimultaneous frequency diversity transmits duplicate information onmultiple carriers. For example, data to be sent by a base station 102 toa remote station 104 is transmitted at a first frequency f₁ (signal 202)and at a second frequency f₂ (signal 204). The two frequencies f₁ and f₂should be chosen such that they fade independently. For example,frequencies f₁ and f₂ can be chosen to be greater than 20 MHz apart sothat the likelihood of both channels fading simultaneously is reduced.The frequency separation is implementation-dependent and is affected bya variety of technical and regulatory factors.

In most radio communication systems 100, signals are processed at lowerfrequencies than their transmission frequencies, decoupling signalprocessing from transmission. A local oscillator (LO) may be used togenerate a signal that is mixed with a data signal to raise itsfrequency to the transmission frequency. If signals 202 and 204 are toofar apart, two LOs may be used with one LO used to generate signal 202and a second LO to generate signal 204.

So that a remote station 104 does not require simultaneous reception ofsignals 202 and 204, duplicate information may be transmitted on two ormore independently fading carrier frequencies at different points intime. By transmitting signal 202, waiting a period of time, and thentransmitting signal 204 at a second frequency, a radio communicationsystem 100 may employ non-simultaneous frequency diversity such thatonly a single receive path is required, thereby reducing the complexityand expense of both the base station 102 and the remote stations 104.

Referring to FIGS. 3A and 3B, a radio communication system 100 usingnon-simultaneous frequency diversity transmits a signal 302 at a firstfrequency f₁ at time T₁ and then transmits a signal 304 containingduplicate information at a second frequency f₂ at time T₂. These figuresonly show the amplitude and frequency components of signals 302 and 304;however, they also may include a phase component. The signal 304duplicates at least some of the information included in signal 302;however, the information may be encoded differently so that the signals302 and 304 do not have identical amplitudes and phases.

By transmitting duplicate information at different frequencies,non-simultaneous frequency diversity provides many of the benefits ofsimultaneous frequency diversity without necessitating simultaneousreception. When changing transmission and reception frequencies, somedelay is needed to allow the frequency adjustments to settle. The timeelapsed between T₁ and T₂ is predetermined and may be based on theneeded delay.

In the examples described above, information is transmitted twice toimplement non-simultaneous frequency diversity. However, the informationmay be transmitted any number of times. Additional redundanttransmissions may further improve performance at the expense ofbandwidth.

Redundant information may be simply retransmitted, or the radiocommunication system 100 may apply a complex gain, varying the phaseand/or amplitude of the redundant signals. A receiving device maycombine the two or more received transmissions, possibly resulting insignal gain.

Referring to FIG. 3C, if significant delay is needed between frequencychanges, it may be advantageous to transmit multiple signals at thefirst frequency f₁ with a short delay T_(i) between transmissions andthen transmit duplicate information at the second frequency f₂ after adelay T_(d). Any values may be chosen for delays T_(i) and T_(d);however, less time is usually needed between transmissions at a singlefrequency or at nearby frequencies, so T_(i) is typically smaller thanT_(d). In this example, three signals 322, 324, and 326 are sequentiallytransmitted at frequency f₁. Then, after a delay T_(d), three signals328, 330, and 332 are sequentially transmitted at a second frequency f₂.

The examples of non-simultaneous frequency diversity described aboveillustrate the technique in a single-carrier transmission. Some moderncommunication systems employ multiple-carrier technology, such as, forexample, spread spectrum, frequency division multiplexing, andorthogonal frequency division multiplexing (OFDM). Instead oftransmitting a signal modulated at a single carrier frequency, amulti-carrier transmission system sends a signal across a widercommunication channel, with portions of the signal modulated at varioussub-carrier frequencies.

For example, an OFDM communication system transmits an informationstream across a wideband channel (e.g., 20 MHz channel) that is dividedinto many narrow sub-channels. The information stream is broken intoblocks such that multiple blocks may be modulated at various sub-carrierfrequencies and transmitted across the sub-channels. Each blocktransmitted at a sub-carrier frequency is called a tone. For example,the IEEE 802.16 standard provides for an OFDM implementation using awideband channel having many as 2048 tones.

In a multi-carrier system, a transmitted signal spans multiplefrequencies. To implement non-simultaneous frequency diversity in amulti-carrier system, information transmitted in a first signal (e.g.,one or more tones from an OFDM transmission) is transmitted in a secondsignal at a later point in time. The information may be encodeddifferently from the first transmission to the second transmission. Forexample, the system may apply a complex gain, rearrange portions of theinformation, or otherwise transform the information such that areceiving system can recover the transmitted information from one ormore of the received signals. Because OFDM signals span multiplefrequencies, duplicate information may be transmitted on different tones(i.e., modulated at a different sub-carrier frequency) and/ortransmitted on different channels (i.e., modulated to a frequencyoutside the wideband channel of the first transmission).

Referring to FIG. 4A, a transmitted OFDM channel 402 includes multipleblocks of data spread across a range of frequencies (i.e., tones). TheOFDM system may be extended to incorporate frequency diversitytechniques by transmitting duplicate information in a second OFDMchannel 404. If the second OFDM channel 404 is transmitted at a secondpoint in time, then the radio communication system employsnon-simultaneous frequency diversity.

Referring to FIG. 4B, an OFDM radio communication system transmitsmultiple blocks of data simultaneously across multiple frequencies.Diagrams 452 and 454 show tones in an OFDM system transmitted atdiffering points in time. Diagram 452 shows data transmitted at a firstrange of frequencies and diagram 454 shows data transmitted at a secondrange of frequencies. In this example, a first OFDM signal is broadcastincluding information “A”, “B”, “C”, and “D”, with “D” transmitted induplicate. At a later point in time, a second OFDM signal is broadcastat a second range of frequencies containing the information “A”, “B”,“C”, and “D” with “C” and “D” duplicated. The information “A” istransmitted at corresponding tones within the channel (i.e., at thefirst data tone of each channel). The information “B” is retransmittedat a different relative location within the channel. The information “C”is transmitted in duplicate (using two separate tones) in the secondchannel. The information “D” is transmitted in duplicate in both thefirst and the second channels. Finally, a third OFDM signal is broadcastusing the first channel with the information “A”. The information may betransmitted any number of times and the system may encode eachtransmission in a different way (i.e., the system may apply a complexgain or otherwise transform duplicate information).

FIG. 4B shows that non-simultaneous frequency diversity may beimplemented in a variety of ways such as, for example, the following:(1) duplicate information transmitted at corresponding frequencies atconsecutive points in time (e.g., “A”); (2) multiple copies of duplicateinformation (e.g., “A”, “C”, and “D”); (3) duplicate informationtransmitted at non-consecutive points in time (e.g., “D”); and (4)information duplicated within a single channel (e.g., “D” and the secondtransmission of “C”).

Referring to FIG. 5A, an implementation of a radio communication system100 using non-simultaneous frequency diversity is built using a radio500 for the base station 102 and remote stations 104. The radio 500includes an antenna 502 for receiving and/or transmitting RF signals, aradio frequency (RF) stage 504 for converting signals betweentransmission frequency and baseband frequency, and a baseband stage 506.

The antenna 502 may be implemented using any conventional technology,such as, for example, a quarter-wave omni-directional antenna. The radio500 may use a single antenna for transmission and reception, or it mayuse multiple antennas to improve performance using beam forming and/orantenna diversity.

In this implementation, signals are processed in software by thebaseband stage 506. The baseband stage 506 includes one or moreintegrated circuits, such as, for example, a digital signal processor(DSP), to implement application logic. In a networking application, theDSP implements the physical layer (PHY), the media access control layer(MAC), and the network layer functions, such as,modulation/demodulation, coding/decoding, and traffic scheduling. Thebaseband stage 506 also may include components to support wireline(e.g., 10/100 Base T), wireless (e.g., 802.11g), phoneline (e.g.,HomePNA), and/or powerline interfaces.

The RF stage 504 includes components to convert signals fromtransmission frequencies to baseband frequencies and vice versa. The RFstage 506 also provides analog-to-digital converters anddigital-to-analog converters so that signals processed by the basebandstage 506 are digital.

Referring to FIG. 5B, the RF stage 504 may be implemented using a localoscillator (LO) 552, an intermediate frequency (IF) receiver 554, and anIF transmitter 556. The LO 552 converts signals between transmissionfrequency and intermediate frequency which are used by the IF receiver554 and the IF transmitter 556. The IF receiver 554 takes the receivedsignal after it has been converted to IF and generates signals forprocessing by the baseband stage 506. The baseband stage 506 sendssignals for transmission to the IF transmitter 556 in the RF stage. TheIF transmitter 556 generates a transmission signal at the intermediatefrequency, which is mixed with a signal from the LO 552 to convert thesignal to transmission frequency.

The local oscillator 552 and IF receiver 554 make up a receive path 558.Because the radio 500 uses non-simultaneous frequency diversity, only asingle receive path is needed. To transmit information at twofrequencies, the IF transmitter 556 provides an RF signal that is mixedwith a signal from the LO 552 to convert the signal to a firsttransmission frequency. Then, the LO 552 may be used to produce a secondsignal to convert the same IF transmitter 556 signal to a secondtransmission frequency. Because the transmissions do not occursimultaneously, multiple IF transmitters 556 are not needed and thesignal may be received using a single IF receiver 554 in a singlereceive path 558. The implementation shown in FIG. 5B is included toillustrate the receive path 558 benefits of non-simultaneous frequencydiversity. In practice, additional components would be included, suchas, for example, various filters, amplifiers, and logic.

If the first and second transmission frequencies vary greatly, the localoscillator 552 may take too much time to settle. One solution is to usemultiple local oscillators 552 with logic provided to select theappropriate LO 552 signal for a particular transmission or reception.Using two LOs 552, a radio 500 may down-convert a first transmissionusing the signal from one LO 552 and down-convert a second transmissionusing the signal from another LO 552. In this manner, the IF receiver554 and the same receive path 558 may be used to provide frequencydiversity.

Referring to FIG. 6A, the techniques described above may be used buildradios employing frequency diversity with a single transmit/receivepath. However, as shown in FIGS. 3A through 3C, this results in somewasted bandwidth as nothing is transmitted at frequency f₂ whileinformation is transmitted at frequency f₁ and vice versa. To makebetter use of available bandwidth while employing non-simultaneousfrequency diversity, a base station 102 may be configured tosimultaneously transmit to multiple remote stations 104. For example,FIG. 6A shows a base station 102 that is operable to transmit to remotestations 602 (designated by a triangle) and 604 (designated by acircle).

Referring to FIG. 6B, the base station 102 when using non-simultaneousfrequency diversity to communicate with remote station 602 transmitsinformation at a first frequency f₁ and then transmits information at asecond frequency f₂. While the base station 102 is transmitting toremote station 602 at the first frequency f₁, the base station 102 maysimultaneously transmit information to another remote station, such as,for example, second remote station 604, at another frequency (e.g.,frequency f₂). Similarly, while the base station 102 transmits to thesecond remote station 604 at frequency f₁, the base station 102 maytransmit to another remote station 104 using frequency f₂. FIG. 6B showsinformation transmitted at frequencies f₁ and f₂ at different points intime. Signals 612, 614, 616, and 618 are each shown with a circle ortriangle corresponding to remote stations 602 and 604 discussed abovewith respect to FIG. 6A. At a first point in time, a signal 612 betweenthe base station 102 and the second remote station 604 (i.e., circle) istransmitted at frequency f₁ while a signal 616 between the base station102 and remote station 602 (i.e., triangle) is simultaneouslytransmitted at frequency f₂. After time T_(i), the frequency use isreversed with a signal 614 between the base station 102 and remotestation 602 (i.e., triangle) is transmitted at frequency f₁ while asignal 618 between the base station 102 and remote station 604 (i.e.,circle) is simultaneously transmitted at frequency f₂. This techniquemay be employed to make better use of available bandwidth withnon-simultaneous frequency diversity.

In the example discussed above, a base station 102 simultaneouslycommunicates with remote stations 602 and 604. A remote station 104using non-simultaneous frequency diversity communicates with the basestation 102 using at least two frequencies and the remote station 104does not simultaneously send and/or receive at the two frequencies.Instead allowing bandwidth to go unused, the base station 102 makes useof the otherwise idle bandwidth to communicate with another device. Inthis example, the base station 102 uses the two frequencies tocommunicate with two devices; however, this frequency may be used in awide variety of ways.

For example, a group of n devices may be assigned to share a group of ffrequencies. For each point in time, the frequencies are allocated amongsome or all of the devices such that each device is able to determinewhen to transmit and/or receive at a particular frequency. This becomesa standard communication scheduling problem. It may be desirable toequitably allocate frequency usage to each of the n devices or it may bedesirable to prioritize based on the device and/or the content or typeof the communications. Any scheduling techniques may be used allocatethe available bandwidth such that devices may employ non-simultaneousfrequency diversity.

In one implementation, a group of 4 devices (A, B, C, and D) share 3frequencies (1, 2, and 3). For example, device A may communicate atfrequency 1 (i.e., A1) while device B communicates at frequency 2 (i.e.,B2). Bandwidth utilization is scheduled such that each device gets anequal portion of the available bandwidth. Table T1 below shows bandwidthscheduling at various points in time. TABLE 1 Time Schedule 1 A1,B2,C3 2B1,C2,D3 3 C1,D2,A3 4 D1,A2,B3

Any alternative scheduling could be used; however, using the scheduleshown in Table 1, each of the remote devices A, B, C, and D need only asingle transmit/receive path. The base station 102, on the other hand,may use multiple transmit/receive paths to support three simultaneouscommunications at frequencies 1, 2, and 3. It should be understood thatfrequencies 1, 2, and 3 may each constitute a single frequency, or theymay each include a range of frequencies for multi-carrier transmissions.Both transmit and receive times typically are scheduled. For example, abase station 102 communicating at two simultaneous frequencies maysimultaneously transmit, simultaneously receive, or may transmit at onefrequency while receiving at another.

Referring to FIG. 7A, a base station 102 may transmit multi-connectionsignals using non-simultaneous frequency diversity by first identifyinga first piece of information the information to be transmitted (702). Ina network implementation, the data link layer breaks information intoframes for transmission across the physical layer. In thisimplementation, the information to be transmitted includes a singleframe. The size of a frame may be dependent on link quality—if linkquality is high, more information may be transmitted at each frequency;however, as link quality degrades, less and less information may bedifferentiated in a received signal. The information is then transmittedat a first frequency (704) while the base station simultaneouslycommunicates at a second frequency. This simultaneous communication mayinclude transmitting to another remote device 104 at the secondfrequency and/or receiving from another remote device 104 at the secondfrequency.

The system then waits a predetermined amount of time before transmittingduplicate information (706). The amount of time to wait may be fixed ordynamic. If the wait time is fixed, it is best to choose the leastamount of time such that the system can transmit at a differentfrequency. After a predetermined amount of time (706), the systemtransmits duplicate information at the second frequency (708). Theduplicate information may be identical to the information initiallytransmitted, or it may be encoded differently. Any coding techniques maybe used so long as the receiving device is able to obtain thetransmitted information from both the first and the second transmissions(if both are received correctly). While transmitting at the secondfrequency, the base station 102 also may communicate with another remotedevice 104 by transmitting or receiving information at another frequency(e.g., at the first frequency).

In a broadband wireless implementation, multiple base stations 102 aredistributed through a service area. These base stations and theirantennas may be placed, for example, on towers, utility poles, orbuildings. Throughout the service area, customers may install subscriberstations (remote devices 104) that may be used to communicate with abase station 102 to enable Internet access. In this implementation, RFsignals are affected by a variety of man-made and natural objects,causing multipath interference and fading. To improve performance, thissystem uses OFDM and non-simultaneous frequency diversity. To implementnon-simultaneous frequency diversity, the base station 102 communicateswith the remote devices using multiple frequencies. The communicationsmay be scheduled such that all allocated bandwidth may be used at anypoint in time. In other words, a remote device 104 and a base station102 communicating with non-simultaneous frequency diversity overmultiple frequencies, may be using one frequency at a time. The unusedfrequencies may be scheduled for use with other remote devices 104 toimprove bandwidth utilization.

Referring to FIG. 7B, a base station 102 receives a signal transmittedusing non-simultaneous frequency diversity by first receiving a firstsignal transmitted at a first frequency while simultaneouslycommunicating at a second frequency (752). After a predetermined amountof time, the system receives a second signal transmitted at the secondfrequency (754). The waiting period may be fixed or may be dynamicallyadjusted based on system performance.

Once the first signal and second signals have been received, the systemidentifies the transmitted information based on the two signals (756).Any diversity combining technique may be used to identify thetransmitted signal including: selection diversity, equal gain combining,and maximal ratio combining. Using selection diversity, the systemsimply uses the strongest signal (i.e., the one with the highestsignal-to-noise ratio). Using equal gain combining, signals are linearlyadded. Using maximal ratio combining, weights are calculated to combinethe received signals to maximize the signal-to-noise ratio.

Referring to FIG. 7C, a remote device 104 may receive information in amulti-connection radio system using non-simultaneous frequency diversityby receiving a first signal transmitted at a first frequency while asecond device communicates at a second frequency (762). The seconddevice may communicate by transmitting or receiving information with thesame base station 102 that the remote device 104 is communicating withor another base station 102. After a predetermined amount of time, theremote device 104 receives a second signal transmitted at the secondfrequency (764). While the second signal is being received, otherdevices may be using the first frequency. Once the first signal andsecond signals have been received, the system identifies the transmittedinformation based on the two signals (766).

In one implementation, the radio communication system 100 providesbroadband wireless Internet services (based on the IEEE 802.16standard), enabling remote devices 104 to access the Internet (network106) through the base station 102. The remote devices 104 (also calledsubscriber units) may be deployed to customer's homes to enablehigh-speed Internet access similar to that provided by DSL or cable.Many wireless network systems employ orthogonal division multiplexing(OFDM) because it provides high spectral efficiency by spreading signalsacross a block of frequencies. In this implementation, OFDM is usedalong with non-simultaneous frequency diversity to improve performance.

Non-simultaneous frequency diversity may be used in any wirelesstechnology to improve system performance without requiring that twodisparate RF signals be received at the same time. A number ofimplementations have been described. Nevertheless, it will be understoodthat various modifications may be made without departing from the spiritand scope of the invention. Accordingly, other implementations arewithin the scope of the following claims.

1. A radio communication system comprising: a remote device radio; and abase station radio operable to communicate with the remote device radioat a first channel and at a second channel using non-simultaneousfrequency diversity, wherein the base station is operable to communicatewith a device other than the remote device at the second channel whilethe remote device radio and the base station radio are communicating atthe first channel.
 2. The radio communication system of claim 1 whereinthe remote device radio is a subscriber station in a wireless network.3. The radio communication system of claim 1 wherein the base stationradio is a base station in a wireless network.
 4. The radiocommunication system of claim 1 further comprising a second remotedevice radio such that the base station radio is operable to communicatewith the remote device radio at the first channel while communicatingwith the second remote device radio at the second channel.
 5. The radiocommunication system of claim 1 wherein the remote device radio includesa single transmit/receive path.
 6. The radio communication system ofclaim 1 wherein the frequency separation between the first channel andthe second channel is at least 20 MHz.
 7. The radio communication systemof claim 6 wherein the information transmitted on the first channel andthe information transmitted on the second transmission channel differ bya complex gain.
 8. The radio communication system of claim 1 wherein thefirst transmission channel and the second transmission channel arewideband channels.
 9. A radio using non-simultaneous frequencydiversity, the radio comprising: an antenna; a radio frequency modulecoupled to the antenna such that the radio frequency module is operableto transmit or receive radio frequency signals at a first channel andsignals at a second channel using the antenna; and a baseband modulecoupled to the radio frequency module, the baseband module operable totransmit or receive signals through the radio frequency module, suchthat signals transmitted or received by the radio employnon-simultaneous frequency diversity using the first channel and thesecond channel, wherein additional devices are operable to use thesecond channel while the radio is transmitting or receiving radiofrequency signals at the first channel.
 10. The radio of claim 9 furthercomprising a second antenna coupled to the radio frequency module. 11.The radio of claim 9 wherein the radio frequency module comprises: alocal oscillator operable to generate a signal; and a zero-if mixercoupled to the local oscillator such that the zero-if mixer is operableto convert signals from baseband frequencies to transmission frequenciesusing the local oscillator.
 12. The radio of claim 9 wherein the radiofrequency module comprises: a local oscillator operable to generate asignal; an intermediate frequency receiver; an intermediate frequencytransmitter; a receive mixer coupled to the intermediate frequencyreceiver and the local oscillator; and a transmit mixer coupled to theintermediate frequency transmitter and the local oscillator, wherein thereceive mixer and the transmit mixer convert signals between anintermediate frequency and a transmission frequency using the localoscillator signal.
 13. The radio of claim 12 wherein the radio isoperable to transmit data using non-simultaneous frequency diversity byusing the local oscillator to transmit data at a first frequency and byusing the local oscillator to transmit data at a second frequency. 14.The radio of claim 12 wherein the receive mixer, the local oscillator,and the intermediate frequency receiver form a receive path such thatthe radio employs non-simultaneous frequency diversity using a singlereceive path.
 15. The radio of claim 12 further comprising a secondlocal oscillator such that the radio is operable to transmit data usingnon-simultaneous frequency diversity by using the local oscillator totransmit data at a first frequency and by using the second localoscillator to transmit data at a second frequency.
 16. The radio ofclaim 9 wherein the baseband module uses orthogonal frequency divisionmultiplexing (OFDM).
 17. A method for transmitting information usingnon-simultaneous frequency diversity comprising: identifying informationto be transmitted to a first device; transmitting the identifiedinformation to the first device on a first channel while simultaneouslycommunicating with a second device on the second channel; and after apredetermined amount of time, transmitting the identified information ona second channel.
 18. The method of claim 17 wherein identifyinginformation to be transmitted includes identifying a block to betransmitted from a set of information to be transmitted.
 19. The methodof claim 18 wherein the block includes no more than the maximum amountof information that can be transmitted at one time.
 20. The method ofclaim 19 where the size of the block is based on the number oforthogonal frequency division multiplexing (OFDM) tones.
 21. The methodof claim 17 wherein transmitting the identified information to the firstdevice on a first channel includes mixing an intermediate frequencysignal with the output from a local oscillator to convert theintermediate frequency signal to the transmission frequency of the firstchannel.
 22. The method of claim 21 wherein transmitting the identifiedinformation at a second frequency includes mixing an intermediatefrequency signal with the output from a local oscillator to convert theintermediate frequency signal to the transmission frequency of thesecond channel.
 23. A method for receiving information transmitted usingnon-simultaneous frequency diversity comprising: receiving a firstsignal transmitted by a first device on a first channel whilesimultaneously communicating with a second device on a second channel;after a predetermined amount of time, receiving a second signaltransmitted by the first device on the second channel; and identifyingtransmitted information based on the first signal and the second signal.24. The method of claim 23 further comprising converting the firstsignal to an intermediate frequency using a signal from a localoscillator.
 25. The method of claim 24 further comprising converting thesecond signal to an intermediate frequency using a signal from a localoscillator.
 26. The method of claim 25 wherein the same local oscillatoris used to convert the first signal to an intermediate frequency and toconvert the second signal to an intermediate frequency.
 27. The methodof claim 23 wherein the predetermined amount of time is fixed.
 28. Themethod of claim 23 wherein a single receive path is used to receive thefirst signal transmitted on the first channel and to receive the secondsignal transmitted on a second channel.
 29. The method of claim 23wherein the first channel and the second channel are wideband channels.30. The method of claim 23 wherein the first channel and the secondchannel differ by at least 20 MHz.
 31. The method of claim 23 whereinidentifying transmitted information based on the first signal and thesecond signal includes combining the first signal and the second signalusing selection diversity.
 32. The method of claim 23 whereinidentifying transmitted information based on the first signal and thesecond signal includes combining the first signal and the second signalusing equal gain combining.
 33. The method of claim 23 whereinidentifying transmitted information based on the first signal and thesecond signal includes combining the first signal and the second signalusing maximal ratio combining.
 34. A method for receiving informationtransmitted using non-simultaneous frequency diversity comprising:receiving a first signal transmitted by a first device on a firstchannel while a second device communicates on a second channel; after apredetermined amount of time, receiving a second signal transmitted bythe first device on the second channel; and identifying transmittedinformation based on the first signal and the second signal.
 35. Themethod of claim 34 wherein the first device is a base station.
 36. Themethod of claim 35 wherein the first signal transmitted by a firstdevice is received while the second device communicates with the firstdevice.